1. Field of the Invention
The present invention relates to wood waste burning systems, and somewhat more particularly to an improved grating structure for use in a furnace means charged with wet or dry wood waste materials.
2. Description of the Prior Art
Particulate wood waste materials, such as sawdust, hogged bark, wood chips, shavings, green twigs and the like are produced in large quantities in many industries. Disposal of such materials, particularly if it is moist or wet, in an efficient and pollution-free manner is a serious problem in such industries. Because such waste wood materials generally occupy a substantial volume and such materials are a potentially valuable heat source, disposal is generally undertaken by means of combustion.
In order to dispose of a high volume of wood waste materials in an efficient manner, a furnace for burning such materials must be capable not only of accommodating a large volume of material but must also be able to uniformly raise the temperature of such material to a level at which optimum combustion can occur and be able to supply adequate air or oxygen to allow complete combustion to occur. If the temperature achieved is too low to effectuate proper combustion, only a portion of the material to be disposed will burn, thereby not only diminishing disposal efficiency, but also requiring that the furnace be cleansed more frequently than if complete combustion occurred. If insufficient oxygen or air is supplied to the combustion chamber, a similar problem occurs.
A further aggravating fact in the disposal of waste wood materials is that frequently such materials are green, damp or even wet and thus must first be dried, then heated and finally ignited before complete combustion of such material can occur. This requires a relatively steep temperature gradient within the combustion chamber of a furnace so as to avoid undue delays between drying and ignition.
In addition to achieving a proper temperature in a furnace, other factors contribute to efficient and pollution-free burning of wood waste material, such as the rate at which such material is fed to the furnace, the material-to-air ratio in the material stream being charged to the combustion chamber and the amount of air turbulence available within the combustion chamber for uniformly heating, drying and igniting the material. A controlled wood waste burning system capable of monitoring and cooperatively adjusting each of these factors is disclosed and claimed in our U.S. Pat. No. 4,311,102 the teachings of which are incorporated herein by reference. The system disclosed in the patent comprises a rotary screw conveyor for bottom unloading of a waste wood material storage bin, a sensor monitoring material levels in the bin, a choke screw device for transferring a select amount of the waste material to a transport system comprising a rotary feed, which transfer a constant amount of the particulate material from the choke screw to a transport conduit, an adjustable blower which provides a select volume of air to the conduit to entrain the material deposited therein at an optimum material-to-air ratio, a furnace means fed by such conduit and wherein the material is combusted, along with integrated control circuitry for optimum operation of the overall system.
A typical present-day wood waste burning furnace means comprises an enclosed relatively large-volume chamber lined with a fire-resistant material and connected to a chimney stack. A relatively large volume of wood waste material to be burned is either manually or automatically loaded onto the floor of such chamber, doused with a flammable liquid, such as kerosene or oil, ignited and allowed to smolder for an indefinite period of time. This type of operation is ineffective to fully extract the maximum amount of heat energy in the wood material, produces excessive ashes, smoke and other pollutant in the chimney which contaminate the atmosphere and produces large amounts of solid combustion products that require furnace shut-down every one or two loading cycles for manual clean-out thereof. While other furnace systems are known, they typically cannot accommodate large volumes of waste wood products, particularly when such products are moist or damp.